A semitone is the smallest interval between pitches. On a piano keyboard, a white key and the black key next to it, or a white key next to another white key where there is no black key between them, are a semitone apart. A whole tone is two semitones, the distance from C to D for example.
Semitones and whole tones on the keyboard
C to C♯ is a semitone, and C to D is a whole tone. There is no black key between E and F or between B and C, so those adjacent white keys are a semitone apart. A DAW’s piano roll uses the same layout as a keyboard, so you can see semitones and whole tones with your eyes.
The material scales are made of
The character of a scale is determined by how semitones and whole tones are ordered. A major scale, for example, is built from the pattern whole, whole, half, whole, whole, whole, half. Change the order and you get a different scale, such as a minor or a pentatonic scale.
The relationship with intervals
An interval, which expresses the distance between two notes, can be worked out from how many semitones are stacked up. When you transpose or modulate up a semitone, you move every note by one semitone.
Where you meet it in music production
Settings where +1 in pitch raises the sound a semitone and +12 raises it an octave are very common. When you transpose loop material, move it in semitone steps and check by ear that it fits the key and the chords.
Start by playing neighboring notes
Before the theory, the quickest route is to play C and C♯, then C and D, one after another in the piano roll. Once you can hear the difference in distance, explanations of scales and chords become much easier to follow.
